1. Field of the Invention
The present invention relates to a sheet remaining amount detection device applied to a sheet feeding mechanism constructed such that a tray bearing sheets is moved upward by taking up a rope (e.g. wire rope) on a take-up pulley, and an image forming apparatus including such a device.
2. Description of the Related Art
Recently, sheet feeding mechanisms which stock a relatively large number of sheets and feed these sheets have been widely used. A sheet feeding mechanism having the following construction has been proposed as such a sheet feeding mechanism.
Upon feeding sheets placed on a sheet tray, the sheet tray is moved upward so that the uppermost one of the sheets is located at a preset feeding position. A wire is fixed to the sheet tray, which is moved upward by taking up the wire using a drive force of a motor.
After being located at a predetermined lowest position, the sheet tray is so moved upward that the uppermost sheet on the sheet tray is located at the feeding position and the number of revolutions of the motor in the process of moving the sheet tray upward is counted. Based on the count value, the remaining amount of sheets on the sheet tray is detected.
However, since the count value on the number of revolutions of the motor is stored in a memory such as a DRAM in the above conventional sheet feeding mechanism, the count value stored in the memory is cleared if a power supply for the sheet feeding mechanism is disconnected.
Thus, the present position of the tray is not known when the sheet feeding mechanism is restarted, wherefore the present position of the tray has to be confirmed by lowering the sheet tray to the lowest position again, moving the sheet tray upward until the uppermost sheet on the sheet tray reaches the feeding position and counting the number of revolutions of the motor at that time. Power consumption is wasted if the sheet tray is moved upward and downward again in this way.